A plurality of buttons is equipped on the top surface of a portable radiotelephone. A button cover covering the buttons is prepared to prevent the buttons of the radiotelephone from being accidentally operated by the unintentional exertion of force. The button cover may rotate between a first position covering the buttons and a second position allowing a user to push one of the buttons, which is known in the art.
The button cover structure of the portable radiotelephone should be designed for a user to use conveniently. For this, a hinge device is provided to make the button cover move automatically toward either the first or second position.
Manufacturers have tried to reduce the volume, size and weight of the portable radiotelephone. The more the radiotelephone is miniaturized, the more it needs to be easily manufactured. Thus, it is desirable that the hinge coupling a body of the radiotelephone with the button cover is modulated and miniaturized. The modulated hinge device is required to have the structure for holding moving parts of the hinge, such as a cam member, a cam follower and a spring. For miniaturization, the size and the number of parts of the holding structure should be reduced.
The relative motion between the cam member and the cam follower of the hinge is required to be smoothly done. Additionally, when the cam follower slides along the cam surface, it should be guided stably.